Following John's strategy: make those spawn bosses wander back and forth by changing the maze ...
The other thing I did was to upgrade my frost at just the right time so the two spawn bosses would be closer to each other ... plus with the timing just right, the spawn bosses would be hanging out far away from my squirt barrage when the big flying bosses showed up. So now the squirts focus on the flyers - I'll deal with the spawn later!